The number of users in cellular systems has significantly increased. Accordingly, systems of 5th Generation have been increasingly demanded. Shifting from 4th Generation to 5th Generation demands some breakthroughs (e.g., improvement of both spectral efficiency and energy efficiency, and advanced radio frequency domain processing).
From the viewpoint of an improvement in spectrum efficiency, a multiple access technology (MAT) is one of the important elements. As multiple access technologies, interleave division multiple access (IDMA), filter bank multicarrier (IDMA), filter bank multicarrier (FBM), and non-orthogonal multiple access (NOMA), and the like can be considered. In particular, in IDMA systems, interleavers can distinguish different users from each other and efficiently remove interference between the users. Accordingly, design of interleavers is one of the most important elements in an IDMA system. Each user uses an interleaver unique to the user. As an interleaver becomes longer, correlation with an interleaver of a different user becomes lower, data of the different user can be detected more easily, and performance of a bit error rate (BER)/block error rate (BLER) becomes more preferable.
For example, Non-Patent Literatures 1 to 5 have proposed interleavers for IDMA systems. Specifically, Non-Patent Literature 1 proposes a pseudo-random interleaver (PRI), Non-Patent Literature 2 proposes a power interleaver (PI), Non-Patent Literature 3 proposes a helical interleaver (HI), Non-Patent Literature 4 proposes a deterministic interleaver (DI), and Non-Patent Literature 5 proposes a linear congruential interleaver (LCI).